1. Field of the Invention
The present invention relates to an optical information recording apparatus which can appropriately process diffracted light of reflected light from a DMD(DIGITAL MICRO MIRROR DEVICE) when the DMD™ is used as a spatial light modulator.
2. Description of the Related Art
In general, holographic recording which records information in a recording medium by utilizing holography is performed by overlapping information light carrying image information and reference light inside the recording medium and writing resultant interference fringes in the recording medium. When the recorded information is reproduced, the recording medium is illuminated with reference light to cause diffraction attributable to the interference fringes which reproduces the image information.
In order to generate the information light carrying the image information, light is spatially modulated by optical intensity. For example, in Japanese Unexamined Patent Application Publication No. H11-311938, there are descriptions regarding the holographic recording and light modulation. According to this Japanese Unexamined Patent Application Publication No. H11-311938, descriptions are given that a liquid crystal device can be used for the light modulation.
Here, as a device to spatially modulate light, it is thinkable to use a DMD™. This DMD™ can reflect incident light, changing reflection directions thereof every pixel.
The DMD™ is, however, an aggregation of fine mirrors having a cycle structure. Therefore, the DMD™ forms kind of a diffraction grating. Therefore, redundant diffracted light also exits from the DMD™. When such redundant diffracted light is used as information light, holography required for recording information becomes too large, and a recording capacity of the recording medium becomes decreased. Shutting out the diffracted light prevents the holography from becoming too large. In this case, however, since light is shut out, the information light becomes dark, and efficiency to utilize the information light becomes low.
As above, when the DMD™ is used as a device to spatially modulate light, there is a problem that the diffracted light of reflected light is hard to be processed.
In order to resolve the foregoing problem, it is thinkable that part of the diffracted light of the reflected light is removed by providing a diffracted light removal means such as a diaphragm in the middle of the information light.